1. Field of the Invention
The application is directed to a heating system for an operator cab in mobile hydraulically operated construction equipment, where the engine coolant circuit provides heat to the operator's cab. In particular, the application is directed to an auxiliary hydraulic circuit that rapidly warms the operator cab in an idle period when main crane functions are not being operated.
2. Background Art
Heavy construction equipment, such as a mobile hydraulic crane, for outdoor use are provided as a superstructure unit having an engine and a cab on a common platform, or a carrier unit having an engine and a superstructure unit having the cab. In the later case, the superstructure unit is usually rotatable upon the carrier unit. In either configuration, the superstructure unit consists of the hydraulic crane. Also, depending on the configuration, either the carrier unit or the superstructure unit may include a pair of crawlers or axles and tires.
The cab is an enclosed area where an operator can control the crane. The operator's cab is heated using a heater located in an engine coolant circuit.
The power system for the crane is hydraulic. In the hydraulic system, an engine powers a hydraulic pump that in turn drives an actuator (such as a motor or cylinder) associated with various mechanical subsystems. The actuators translate hydraulic pressure forces to mechanical forces thereby imparting movement to the mechanical subsystems of the crane.
The hydraulic system can be one of two types—open loop and closed loop. Most hydraulic cranes primarily use an open loop hydraulic system. In an open loop system, hydraulic fluid is pumped (under high pressure provided by the pump) to the actuator. After the hydraulic fluid is used in the actuator, it flows back to a reservoir before it is recycled by the pump. The loop is considered “open” because the reservoir intervenes on the fluid return path from the actuator before it is recycled by the pump. An open loop system having a single pump maintains pressure sufficient to drive the fully loaded mechanical subsystems. An efficient type of open loop system is a load sensing, open loop system.
In conventional heavy construction equipment for outdoor use, when the engine is started then idled for an extended period of time, the engine coolant will be below a temperature necessary to heat the operator's cab. Subsequently, for operation in cold climates, typically auxiliary heaters fueled by propane or diesel fuel are used to provide heat to the cab. Some conventional heavy construction equipment heat the cab using heat generated from operation of the hydraulic equipment. However, propane or diesel fueled heaters pose safety hazards, and hydraulic heaters are large, inefficient and expensive. Also, heating systems that obtain heat from the hydraulic system are complex.
Prior art examples that disclose heating the cab directly from the hydraulic circuit are provided in U.S. Pat. Nos. 5,318,100; 5,085,269; 4,352,456; 4,432,493; 4,192,456. Another prior art example, U.S. Pat. No. 5,024,377, provides heat from an automatic transmission. A further prior art example, U.S. Pat. No. 5,085,269, provides heat by a dedicated heat pump.
However, none of the prior art examples provide heat to a cab during periods when the construction equipment engine is in idle and main crane functions are not being operated, and without stand-alone propane or diesel heaters.